1. Field of the Invention
The present invention generally relates to an electronic assembly, in particular, to an electronic assembly capable of lowering electromagnetic interference.
2. Description of Related Art
In recent years, with the upgrading of the integration of an Integrated Circuit (IC), a Central Processing Unit (CPU) with a high computing speed and a high frequency IC have been widely applied in various types of electronic products. However, such electronic devices have high power consumption. Therefore, to maintain a normal working temperature, a heat dissipation fin set is usually equipped to lower the temperature of the electronic devices.
Generally speaking, the heat dissipation fin set is directly disposed on a chip, and each heat dissipation fin of the heat dissipation fin set may be regarded as a monopole antenna. A conventional heat dissipation fin set is not connected to a grounding layer of a printed circuit board below the chip, and thus could be regarded as a floating metal. In this way, noises are generated by the chip and are further coupled to the heat dissipation fin set. When the frequency of the noises is close to a resonant frequency of the heat dissipation fin set, the heat dissipation fin set becomes a good antenna structure, which not only has strong electromagnetic radiations, but also can be coupled to other external circuits. Therefore, interference is caused to the whole electronic product.
In order to solve the above problem, a method is provided by the prior art that, the heat dissipation fin set is electrically connected to the grounding layer of the printed circuit board, so that a potential difference between the heat dissipation fin set and the grounding layer is lowered, and the electromagnetic radiations are reduced. However, the circuit layout on the periphery of the chip is dense, so it is not easy to find appropriate grounding points on the printed circuit board. In addition, if noises of the grounding point are excessively high, it is even easier for the noises to be coupled to the heat dissipation fin set, thereby enhancing the effect of the electromagnetic radiations.
Another conventional method is to add a metal shielding cover above the heat dissipation fin set to reduce the electromagnetic interference. The main function of the heat dissipation fin set is to conduct the heat generated by the chip out. However, when the heat dissipation fin set is shielded by the metal shielding cover, the heat dissipation effect of the heat dissipation fin set may be largely reduced. If an opening is disposed on the metal shielding cover to expose a part of the heat dissipation fin set in order to solve the problem of heat dissipation, the shielding effect of the metal shielding cover is also lowered.